Day 75 of the BP oil disaster. I’m visiting Boston’s park system, where Olmsted’s innovative Back Bay Fens — in particular — is a reminder that there are environmental solutions as well as environmental problems.

It’s now long forgotten, but the original purpose in creating a park here was to attend to an environmental mess. By the mid-1800s century, this area was a tidal flat where Boston’s sewage pooled and festered. The city decided to try to hold a park-design contest. The winner was a local florist who proposed to turn the area into an ornamental garden — nice notion.

Only problem: the proposed parkland was a wasteland. “Not even eels could live here,” Jeanie Knox of the Emerald Necklace Conservancy told me while showing me around. (Apparently, eels are a kind of environmental bellwether. If you can’t sustain eels, you’re in real trouble.) What’s more, the water was salty. The florist’s park plan, while lovely, simply wasn’t realistic.

Time to call in a park-making expert — Olmsted. Olmsted immediately recognized that this was primarily a sanitation issue. He consulted with city engineers to develop a proper sewage system. He devised various gates and sluices to maintain the water at a constant level. Then he designed a fitting park for the area, a kind of manmade saltwater marsh. He planted appropriate flora: salt hay and cordgrass, rushes and sedges.

In 1910, the Charles River was dammed. Olmsted’s saltwater marsh turned into a freshwater marsh. That required new types of plants. Still, the Back Bay Fens (photo below) maintains much of the character of Olmsted’s original design. BTW, Olmsted dreamed up the name Back Bay Fens.

Olmsted did such a good job with the Fens that he was commissioned to design an entire intricate park system for Boston. Spent the rest of my day touring it. Olmsted suggested that this system should be called “The Jeweled Girdle” — not as winning a name as Back Bay Fens. Fortunately, an unknown someone dreamed up the far superior “Emerald Necklace.”

I especially enjoyed Franklin Park. It’s right in the middle of Boston, but wander far enough into it and you can’t even hear traffic noise. Below is Olmsted’s 99 Steps, hidden away in the so-called Wilderness section of Franklin Park.